1. Field of the Invention
The present invention relates to a control device of an automatic transmission for vehicles.
2. Description of the Prior Art
A conventional control device of an automatic transmission for vehicles is disclosed, for example, in Japanese Patent Application Laid-open Publication No. 2-304256. This automatic transmission comprises a main transmission mechanism arranged coaxially with a torque converter and a sub transmission mechanism arranged in parallel with the main transmission mechanism. In this automatic transmission, the control device achieves a plurality of gear positions by engaging and disengaging friction elements such as planetary gear mechanisms, clutches, brakes and one-way clutches.
In the control device of the automatic transmission, an automatic transmission control unit (hereinafter referred to as an ATCU) determines a gear position suitable for driving conditions, and on-off controls solenoid valves in the control device, thereby switching shift valves by an oil pressure supplied through the solenoid valves. The gear positions are changed by supplying and releasing oil pressure to and from friction elements by the shift valves.
An ordinary control device has a parking range, a rear driving range (hereinafter referred to as a R range), a neutral range, an automatic shift driving range (hereinafter referred to as a D range), a 3 range in which a vehicle is driven forward at a first, second or third speed gear position, a 2 range in which the vehicle is driven forward at the first or second speed gear position, a 1 range in which the vehicle is driven forward only at the first speed gear position.
The conventional control device of the automatic transmission switches the gear position from the fourth speed to the third speed by switching the sub transmission mechanism from a direct driven state to a reduction state. More specifically, the control device shifts the gear position from the fourth speed down to the third speed by disengaging a direct clutch that is engaged at the fourth speed gear position and engaging a reduction one-way clutch and a reduction brake that are unengaged at the fourth speed gear position.
An engagement pressure of the reduction brake is controlled by supply and release of an oil pressure due to the gear shift, and also can be controlled gradually for a predetermined time through a reduction accumulator provided in an oil channel which supplies and releases the engagement pressure.
The gear position is shifted from the fourth speed down to the third speed by an automatic down shift in the D range or a manual down shift in a case the 3 range is manually-selected.
Normally, the manual down-shift is performed in such a manner that a driver manually operates a shift lever for the purpose of driving the vehicle with an engine brake being operable. The reduction brake must be engaged upon the disengagement of the direct clutch in order to prevent the delay in functioning the engine brake. In this case, a high back pressure is supplied to the reduction accumulator to generate a high shelf pressure and stroke the reduction accumulator. Since the engagement pressure of the reduction brake is raised quickly, the reduction brake is engaged while the reduction accumulator is stroking. Consequently, the reduction brake is engaged just after the manual down-shift operation.
In the case of the automatic down-shift in the D range, it is necessary to direct the driving power from an input shaft to an output shaft since the driver would not like to drive the vehicle with the engine brake being operable. When the direct clutch is disengaged, the reduction one-way clutch is engaged to carry on the transmission of power for forward driving. This prevents a trouble in the shift even if the engagement of the reduction brake is delayed. Therefore, the back pressure is not supplied to the reduction accumulator, and the reduction accumulator is stroked at a low shelf pressure. The reduction brake engagement pressure is kept low for a predetermined time to delay the engagement of the reduction brake. This surely prevents the shock resulting from the shift.
Either in the manual down-shift or in the automatic down-shift, a line pressure is supplied directly to the reduction brake after a finish of the stroke of the reduction accumulator so that the reduction brake can be kept engaged.
If the R range is selected in the above prior art automatic transmission, the R range pressure is supplied as the back pressure to the reduction accumulator to maintain the state wherein the reduction accumulator has finished stroking. Thus, the line pressure is directly supplied to the reduction brake to cope with a large loaded torque in backward driving. A pressure regulating valve for reducing pressure is provided in an oil channel that supplies the engagement pressure to the low reverse brake in order to adjust the shock resulting from the shift.
However, the engagement pressure of the reduction brake must be kept low for a time required for the shift plus an allowance in order to surely prevent the shock resulting from the shift by delaying the engagement of the reduction brake in the automatic down-shift. The time in which the accumulator can control the oil pressure corresponds to the time in which the accumulator is stroking, and thus depends on the capacity of the accumulator. For this reason, the reduction accumulator must be quite large in order to keep the low engagement pressure of the reduction brake for a sufficient time. On the other hand, the vehicle is recently equipped with an increasing number of devices, and there is a strong requirement for reducing the size of each device. It is therefore necessary to reduce the size of the control device of the automatic transmission.
It is therefore an object of the present invention to provide a control device of an automatic transmission, which prevents the shock resulting from the shift in the automatic down-shift and is capable of quickly changing gear positions in the manual down-shift. It is another object of the present invention to provide a control device of an automatic transmission, which is capable of engaging friction elements by a sufficient engagement pressure in backward driving. It is yet another object of the present invention to provide a small control device of an automatic transmission.
The above objects can be accomplished by providing a control device of an automatic transmission, which comprises a plurality of forward driving gear positions and a backward driving gear position that are achieved by engaging and disengaging a plurality of friction elements and which is capable of changing the plurality of forward driving gear positions by an automatic shift or a manual shift according to driving conditions, the control device of the automatic transmission comprising: a first friction element that is engaged at least at a lowest speed forward driving gear position or at the backward driving gear position; a pressure regulating valve that is connected to an output oil channel connected to a first oil channel connected to the first friction element, a second oil channel supplied with an original pressure, a third oil channel that is drained if the forward driving gear position is designated and that is supplied with a rear range pressure if the backward driving gear position is designated, and a fourth oil channel supplied with an oil pressure for changing pressure regulating state, the pressure regulating valve outputting the rear range pressure to the output oil channel if the third oil channel is supplied with the rear range pressure, outputting an oil pressure regulated to such an extent as not to engage the first friction element to the output oil channel if the third oil channel is drained and the fourth oil channel is not supplied with oil pressure, and outputting an oil pressure regulated according to the oil pressure supplied to the fourth oil channel if the third oil channel is drained and the fourth oil channel is supplied with the oil pressure; a first shift valve that is connected to the fourth oil channel, a fifth oil channel supplied with a control pressure for controlling the pressure regulating valve and a sixth oil channel connected to a timing solenoid valve, the first shift valve supplying a control pressure to the fourth oil channel by connecting the fifth oil channel and the fourth oil channel when the timing solenoid valve is turned off and draining the fourth oil channel when the timing solenoid valve is turned on; a shift control part that keeps the timing solenoid valve on for a predetermined time when the gear position is automatically shifted from a gear position at which the first friction element is unengaged to a gear position at which the first friction element is engaged, and then turns off the timing solenoid valve; and that switches the timing solenoid valve to an OFF state when the gear position is manually shifted from a gear position at which the first friction element is unengaged to a gear position at which the first friction element is engaged; and wherein an oil pressure for engaging the friction element is supplied to the first oil channel from the pressure regulating valve when the control pressure acts on the pressure regulating valve through the fourth oil channel.
Upon automatically shifting from the gear position at which the first friction element is not engaged is to the gear position at which the first friction element is engaged, the shift control part keeps the timing solenoid valve on for a predetermined time after the shift. Thus, the fourth oil channel is drained for the predetermined time after the shift.
At this time, the forward driving gear position is selected, and thus the third oil channel connected to the pressure regulating valve is drained. The fourth oil channel is also drained. No oil pressure is supplied to the third and fourth oil channels. Therefore, the first oil channel is supplied with an oil pressure, which is regulated to such an extent as not to engage the first friction element, from the pressure regulating valve.
On passage of the predetermined time, the shift control part turns off the timing solenoid valve to supply the fourth oil channel with the control pressure, which acts on the pressure regulating valve.
When the control pressure acts on the pressure regulating valve, the first oil channel is supplied with an oil pressure, which is regulated to such an extent as to engage the first friction element, through the pressure regulating valve. Thus, the first friction element for transmitting a reverse driving force is never engaged for the predetermined time after the automatic shift, and is engaged on passage of the predetermined time. This prevents the shock resulting from the shift.
In the case of the manual shift, the timing solenoid valve is turned off immediately after the shift. Thus, the fourth oil channel is supplied with the control pressure from the fifth oil channel, and the control pressure acts on the pressure regulating valve. When the control pressure acts on the regulating valve, the first oil channel is supplied with the oil channel, which is regulated to such an extent as to engage the first friction element, through the pressure regulating valve. Thus, the first friction element is engaged immediately after the manual shift, and this enables the quick change in the gear positions.
If the R range is selected, the rear range pressure supplied to the third oil channel is supplied to the first oil channel through the pressure regulating valve, so that a sufficient engagement pressure can be quickly supplied to the first friction element. It is possible to prevent the shock resulting from the shift in the automatic down shift, quickly change the gear positions in the manual down shift, and engage the friction element by the sufficient engagement pressure in the backward driving with the use of the regulating valve, the shift valves and the timing solenoid valve with a small capacity without using the accumulator with a large capacity as in the prior art. This reduces the size of the control device of the automatic transmission.
According to the second aspect of the present invention, the control device of the automatic transmission further comprises: a second friction element that is unengaged at a gear position at which the first friction element is unengaged and that is engaged at least at one gear position among gear positions at which the friction element is engaged; a seventh oil channel connected to the output oil channel; an eighth oil channel connected to the second friction element; and an oil pressure circuit connecting the seventh oil channel and the eighth oil channel if a gear position at which the second friction element is engaged is designated.
Accordingly, the oil pressure from the output oil channel of the pressure regulating valve is supplied as the engagement pressure to the second friction element at the gear position at which the second friction element is necessary to be engaged. The pressure regulating valve producing the engagement pressure of the first friction element can also be used as the pressure regulating valve reducing the engagement pressure supplied to the second friction element. This further reduces the size of the control device of the automatic transmission.
Depending on the arrangement of the pressure regulating valve, the first oil channel connected to the first friction element may be connected directly to the output oil channel of the pressure regulating valve. Alternatively, the first oil channel may be connected to the output oil channel through the oil pressure circuit.
The original pressure can be supplied to the pressure regulating valve directly or via the oil pressure circuit.